Method and apparatus for deriving useful steam from a fluctuating heat source

ABSTRACT

A method and apparatus for deriving useful steam from a fluctuating source of heat. The apparatus includes a heatexchanger system which operates under conditions of high heat transfer with natural circulation when steam is withdrawn from the system and which requires forced circulation during operation under conditions of low heat transfer. A single high-pressure booster pump installation coacts with the system to provide a supply of new liquid to the system during periods of high heat transfer and to provide forced circulation during periods of low heat transfer, the booster pump installation being operated constantly at its full capacity and controlled to achieve a constant liquid flow through the system under all operating conditions. The booster pumps have their output connected to a jet pump which forms part of the system so that natural circulation can take place through the jet pump while forced circulation can be provided by way of a jet provided in the jet pump by the booster pumps.

United States Patent [72] Inventor Roland Kemmetmueller Pittsburgh, Pa.

[2]] Appl. No. 847,574

[22] Filed Aug. 5, 1969 [45] Patented Sept. 28, 1971 [73] Assignee American Waagner-Biro Company, llnc.

Pittsburgh, Pa.

[54] METHOD AND APPARATUS FOR DERIVING USEFUL STEAM FROM A FLUCTUATING HEAT SOURCE 12 Claims, 4 Drawing Figs.

[52] US. Cl 122/7 R,

[51] Int. Cl. F22b 1/18 [50] Field of Search 122/7, 7 A,

[56] References Cited UNlTED STATES PATENTS 2,704,534 3/1955 Dalin et al. l22/407 3,234,920 2/1966 Kemmetmuller et al. 122/7 Primary Examir't r -Keiineth W. Sprague Att0rneySteinberg and Blake ABSTRACT: A method and apparatus for deriving useful steam from a fluctuating source of heat. The apparatus includes a heat-euchanger system which operates under conditions of high heat transfer with natural circulation when steam is withdrawn from the system and which requires forced circulation during operation under conditions of low heat transfer. A single high-pressure booster pump installation coacts with the system to provide a supply of new liquid to the system during periods of high heat transfer and to provide forced circulation during periods of low heat transfer, the booster pump installation being operated constantly at its full capacity and controlled to achieve a constant liquid flow through the system under all operating conditions. The booster pumps have their output connected to a jet pump which forms part of the system so that natural circulation can take place through the jet pump while forced circulation can be provided by way of a jet provided in the jet pump by the booster pumps.

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SHEET 3 0F 4 cOLD F DNA E) y I 6% INVENTOR liomwp XE WMEll/EILE/Q j ATTORNEYS METHOD AND APPARATUS FOR DERIVING USEFUL STEAM FROM A FLUCTUATING HEAT SOURCE BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for deriving useful steam from a fluctuating heat source.

For example, the method and apparatus of the invention may be applied to a heat-exchanger system such as a wasteheat boiler used in BOF shops or with other metallurgical furnaces. Installations of this latter type have great fluctuations in the intensity of the heat which is supplied to the heatexchanger system. For example, in the case of a BOF installation, during the blow periods of the converter heat at high intensity is delivered to the waste-heat boiler which forms the heat-exchanger system, so that there is a high transfer at this time, while during the off-blow periods there is a relatively low heat transfer. Because it is essential with such systems to provide forced circulation through the system at least during periods of low heat transfer, it is conventional to provide for such a system one pumping installation to provide circulation through the system and a second pumping installation to supply new feedwater to the system in order to replace fluid taken out of the system. This fluid will normally be taken out of the system only during periods of high heat transfer when the fluid is in a condition where it will provide the required steam which is to be used. Therefore one pumping installation will supply new feedwater to the system only during periods of high heat transfer while the other pumping installation will maintain the fluid circulating in the heat-exchanger system which forms the waste-heat boiler in this case. The result is that a large and expensive pumping installation is required simply to provide new feedwater to the system. A second entirely independent pumping installation is required to circulate fluid through the system. The feedwater supply pumps are required to operate against a closed valve during the time when no feedwater is delivered to the system, so that there is a considerable waste of energy, particularly because the feedwater supply pumps must be designed for peak capacity but operate at this latter capacity only for an extremely short time during each operating cycle.

SUMMARY OF THE INVENTION It is accordingly a primary object of the present invention to provide a method and apparatus which will avoid the above drawbacks.

In particular, it is an object of the invention to provide a method and apparatus according to which a single pump installation can be used both for forced circulation and for supplying new feedwater.

Another object of the present invention is to provide a method and apparatus where the single pumping installation operates constantly at full capacity so that the most efficient operation is achieved.

Thus, it is an object of the invention to provide a method and apparatus capable of achieving useful steam from a fluctuating heat source at a fraction of the cost which is conventionally required for this purpose.

In addition, it is an object of the invention to provide a method and apparatus which take full advantage of the possibility of natural circulation during periods of high heat transfer, so that further savings are achieved in this way.

It is also an object of the invention to provide a method and apparatus which will prevent cavitation effects at the pumps.

Also, it is an object of the invention to provide a method and apparatus according to which a fully automatic operation is achieved.

Yet another object of the invention is to provide a method and apparatus capable of operating with a single heatexchanger system as well as capable of achieving further savings by operation with a pair of heat-exchanger systems.

According to the method of the invention a single high-pressure booster pump installation is constantly operated at fully capacity to provide forced circulation through the heatexchanger system during periods of low heat transfer and to supply new feedwater to the system during periods of high transfer when natural circulation is available while steam is taken from the system. The operations are carried out in such a way that a constant liquid flow is maintained through the heat-exchanger system under all operating conditions.

The apparatus of the invention includes the single pumping unit made up of the high-pressure booster pumps which operate constantly at full capacity and including a jet pump which forms part of the heat-exchanger system and which is connected to the output of the booster pumps. By way of this jet pump it becomes possible to provide natural circulation during periods of high heat transfer when new liquid is supplied to the system by the booster pumps which deliver the new liquid through the jet pump, and at the same time the fluid of the system may be recirculated through the jet pump during periods of low heat transfer to provide forced circulation.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way of example in the accompanying drawings which form part of this application and in which:

FIG. 1 is an example of a prior art installation showing the problems which are solved by the present invention;

FIG. 2 is a schematic illustration of an apparatus of the invention used in connection with a BOF converter;

FIG. 3 shows a variation of the apparatus of FIG. 2, with the schematically illustrated structure of FIG. 3 being shown with an open-hearth furnace as a source of heat; and

FIG. 4 is a schematic representation of the manner in which a pair of heat-exchanger systems may be operated with the apparatus and method of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1, there schematically illustrated therein a heat-exchanger system which includes a waste-heat boiler and which is required to operate under conditions of greatly fluctuating heat intensities. For example, the gas inlet of the waste-heat boiler 1 of the system may receive hot gases from a BOF converter, or from other metallurgical furnaces such as open-hearth furnaces, zinc or copper converters, or any source of heat of greatly fluctuating intensity. For example the heat-exchanger system may be supplied with heat in a wellknown manner from a lime kiln or in a petrochemical plant, for example. In all of these situations the gas inlet into the waste-heat boiler 1 will have periods of high heat intensity alternating with periods of low heat intensity. Thus in the ease of a BOF converter the supply of heat will build up to a very high intensity during the blow periods and will drop off to very low heat intensity during the off-blow periods.

The heat flows upwardly through the boiler to the gas outlets schematically shown in FIG. 1, with heat from the waste gas being delivered to liquid which flows through the boiler pipes in the manner schematically illustrated in FIG. 1.

FIG. 1 show how the heated liquid flows from the boiler to a steam drum 2 with recirculation being derived by way of a circulating pump installation 14. Thus the circulating pumps 14 schematically illustrated in FIG. 1 pump the boiler water from the steam drum 2 through the boiler 1 so as to maintain a forced circulation.

The steam drum 2 communicates with an accumulator 3 from which useful steam is withdrawn as schematically indicated in FIG. I. In the line of communication between the drum 2 and the accumulator 3 there is a back pressure control Naturally, the fluid which is taken from the system must be replaced, and for this purpose a feedwater control valve 7 communicates with the drum 2 and with the outlet of feedwater pumps 9 to deliver feedwater from the tank into the drum 2 during those periods of high heat transfer when the back pressure control valve 5 opens to deliver the stem to the accumulator 3. In this way there is a compensation for the flow of steam to the accumulator and the liquid level in the drum 2 is maintained substantially constant.

In order to achieve this latter type of operation it is essential for the feedwater pumps to be designed to take care of the peak of steam production, although this latter operating condition prevails only for an extremely short time, so that the available horsepower of the motors which drive the pumps 9 is not used all the time, with the pumps 9 operating against a closed valve 7 during periods of low heat transfer when the valve 5 is closed.

In order to avoid the drawbacks of the prior art method and apparatus shown in FIG. 1, the embodiments of the invention illustrated in FIGS. 2-4 may be used.

Referring to FIG. 2, a converter is schematically illustrated with its top open end communicating with the gas inlet for the waste-heat boiler 1. It will be noted that with the arrangement of FIG. 2 the assembly of forced circulating pumps 14 has been completely eliminated. The entire apparatus requires only the single pump installation which includes the high-pressure booster pumps 9. These are identical with the conventional pumps 9 of FIG. 1 so that all of the required operations are derived with the booster pumps which heretofore were required only for supply of feedwater. The pump installation of FIG. 2 includes a jet pump 8 which is connected into the heat-exchanger system and which is also connected to the output of the booster pumps 9. Three pumps are shown so that two can be constantly operated at full capacity with the third pump on standby for the purpose of taking over the operation of one of the other pumps whenever required. These pumps can be driven by electric motors the speed of which can be regulated in any known manner or they may be driven by suitable steam drives which also are capable of being regulated to control the speed of operation of the pumps 9.

The input of the pumps 9 communicates on the one hand with a forced circulation valve means 6 and on the other hand with a feedwater supply valve means 7, the latter being in the form of a nonreturn valve communicating with the feedwater tank 10.

With this arrangement it is possible, for example, to control the valves 6 and 7 manually so that during periods of low heat transfer the valve 7 is closed and the valve 6 is opened to provide forced circulation. At this time the liquid flowing downwardly out of the drum 2 will flow through the forced circulation valve means 6 into the constantly operating pumps 9 to be delivered by the latter in the form ofajet in the jet pump 8 so as to achieve forced circulation in this way. On the other hand, during periods of high heat transfer the valve 6 may be manually closed and the valve 7 manually opened, so that without in any way changing the operating of the pumps 9 it is possible at this time to deliver new feedwater into the system through the jet pump 8 to replace the fluid which is taken out of the system at this time. The heat which is available in the system during periods of high heat transfer will provide a natural circulation through the system so that the pumps 9 can be used at this time together with the jet pump 8 to deliver new feedwater to the system.

While such manual operation is possible, it is preferred to provide a fully automatic operation of the valves 6 and 7, and for this purpose in the line of communication between the drum 2 and accumulator 3 there is an automatic control means 4 which responds to the flow of fluid between the drum 2 and accumulator 3 and which is operatively connected to the valve means 6 and 7 for automatically operating both of these valve means. This automatic control means 4 may take the form of a flowmeter which responds to the fluid flowing through the system to provide closing of the valve 7 and opening of the valve 6 in a fully automatic manner when there is low heat transfer, so that in this way forced circulation is achieved at this time, namely during periods such as startup periods where natural circulation has not yet developed. However, when the steam flow starts out of the dnim 2, the automatic control means 4 responds to open the valve 7 and close the valve 6 so that new feedwater is delivered to the system as the natural circulation develops during periods of high heat transfer. As the natural circulation increases during the increase in the intensity of the heat supplied to the boiler I, the feedwater supply increases to reach a maximum for a short period of time after which the feedwater supply gradually drops off with a gradual dropping off of the natural circulation as the intensity of the heat delivered to the waste-heat boiler drops off. In this way it is possible to achieve a constant balance between natural and forced circulation with the supply of feedwater varying in proportion with the degree of natural circulation and with the forced circulation varying inversely with respect to the natural circulation in such a way that constant flow of liquid through the entire heat-exchanger system is automatically maintained.

Thus, with an arrangement as shown in FIG. 2, during startup the back pressure valve 5 is closed, the feedwater supply valve means 7 is closed, while the forced circulation valve means 6 is open to provide through the booster pumps 9 the forced circulation through the jet pump 8. Thus during these startup conditions of low heat transfer the forced circulation maintains a sufficient quantity ofwater circulating through the system to provide proper operation thereof. When the natural opening pressure is reached the back pressure control valve 5 opened steam flows from the drum 2 into the accumulator 3, with the control means 4 at this time actuating the valves 6 and 7 automatically in the manner described above.

In order to take care ofa condition where an unusually high pressure is reached at the output of the booster pump assembly 9, a nonreturn bypass valve means 20 is provided bypassing the jet pump 8 in the manner shown in FIG. 2 and responding automatically to a given pressure in the output from the pumps 9.

Although it is possible to operate with the apparatus and method described above in connection with FIG. 2, under certain conditions it may be desirable to reduce the possibility of cavitation effects at the pumps 9, and for this purpose an arrangement as shown in FIG. 3 may be used. The method and apparatus of FIG. 3 is identical with that of FIG. 2 except that FIG. 3 shows how the apparatus is operatively connected with an open-hearth furnace and with FIG. 3 a subsidiary heat exchanger 13 is provided between the forced-circulation valve means 6 and the inlet of the booster pump assembly 9. The cold feedwater flows through the heat exchanger 13 to be preheated thereby before reaching the deaerator and feedwater tank 10. As a result it is possible to use the cold feedwater for cooling the forced circulation liquid so as to prevent cavitation in the pumps.

A particularly favorable method and apparatus of the invention is illustrated in FIG. 4. With this method and apparatus there are a pair of heat-exchanger systems communicating with a common accumulator 3, and of course there are no steam drums. A control valve 11 is provided to withdraw the required steam from the accumulator 3 in the manner indicated also in FIGS. 2 and 3. It will be noted from FIG. 4 that while a pair of control means 4 are provided, they both coact with only a single forced circulation valve means 6 and a single supply valve means 7 through which fresh feedwater is supplied from the tank 10. It is also to be noted that a common pipe delivers liquid from the accumulator 3 back into the systems to be circulated therethrough. Also it is to be noted that a single booster pump assembly 9 is provided for both systems while a pair ofjet pumps 8 are provided. This arrangement is possible because the pair of installations are not operated simultaneously in synchronism. In the case of BOF converters, for example, while one converter which supplies heat to one of the systems is in an off-blow condition of low heat transfer the other converter which supplies heat to the other system is in its blow period of high heat transfer, and in this way the systems will alternately be in conditions of high and low heat transfer with the high heat transfer of one system occurring only during low heat transfer of the other system. As a result the extremely economical and highly efficient arrangement of FIG. 4 is rendered possible with the method and apparatus of the invention. It is to be noted that this arrangement also includes the subsidiary heat exchanger 13 for reducing cavitation possibilities, as pointed out above in connection with FIG. 3. Furthermore, it is to be understood that the embodiments of FIGS. 3 and 4 can have bypass valve means in the same way as the embodiment of FIG. 2.

Furthermore, the jet pump 8 is disclosed only schematically in all embodiments. It is possible to achieve further controls for the system by providing the jet pump 8 with a variable throat diameter which can be adjusted to selected size, or interchangeable injection nozzles of different sizes may be provided for the jet pump in a well-known manner.

Thus, with the embodiment of FIG. 4 during startup when there is low heat transfer the pump assembly 9 will pump liquid from the accumulator 3 to whichever one of the systems is in its startup condition of low heat transfer, and the forced circulation requires the water to flow from the valve 6 through a pressure-reducing valve 12 before flowing through the subsidiary heat exchanger 13. In this way'the pressure of the water delivered to the pumps is maintained constant and cavitation effects are avoided. Of course, units 12 and 13 could be eliminated, as indicated in FIG. 2. The jets provided in the pumps 8 during forced circulation maintain a sufficient quantity of water circulating through each system. The arrangement of FIG. 4 automatically adapts itself to the particular conditions of operation according to which to the extent that there is natural circulation in one of the systems, the energy of the pumps 9 is available for forced circulation in the other of the systems with delivery of feedwater automatically taking place in the system where natural circulation occurs in the manner described above.

Thus, it will be seen that with the method and apparatus of the invention it is possible to completely eliminate the circulating pumps 14 of FIG. 1 with the drives therefor, thus decreasing the initial costs as well as the operating costs. The use of the single set of booster pumps for forced circulation as well as for supply of feedwater during peak steam production represents a great economy not only from the standpoint of the saving of equipment but also from the standpoint of the far greater efficiency of operation.

What is claimed is:

I. In a method for operating a heat-exchanger system under greatly fluctuating conditions of high and low heat transfer, the steps of operating the system with at least partial natural circulation during high heat transfer, when fluid is withdrawn from the system, and with forced circulation during periods of low heat transfer, operating a single high-pressure booster pump installation continuously at full capacity while providing said forced circulation through said single pump installation during periods of low heat transfer and while providing a combination of natural circulation and replenishing the liquid of ..the system with said single pump installation during periods of high heat transfer, and providing between the forced circulation and supply of new replenishing liquid to the system, on the one hand, and the natural circulation, on the other hand, a relationship which maintains a substantially constant flow of liquid through the heat exchanger under all operating conditions.

2. In a method as recited in claim 1 and wherein the booster pump installation has suction and discharge sides maintained at a constant differential pressure under all operating conditions.

3. In a method as recited in claim 2 and wherein the speed of operation of the pump installation is regulated to maintain the constant liquid flow in the heat-exchanger system under all operating conditions.

4. In a method as recited in claim 2 and wherein the system includes a jet pump receivitg a jet of liquid from said single pump installation and also receiving and discharging liquid during natural circulation, the step of controlling the operation of said jet pump to contribute to the maintenance of the constant liquid flow through the heat exchanger system.

5. In a method as recited in claim 4, the step of bypassing the jet pump when the pressure of liquid pumped by said single pump installation rises to a given value.

6. In an apparatus for deriving steam from a fluctuating heat source, a heat-exchanger system operating under conditions of great fluctuation between high and low heat transfer, first means for operating the system with at least partial natural circulation during the high heat transfer condition, providing useful steam which can be withdrawn from the system, and second means for operating the system with forced circulation during the low heat transfer condition, said second means including a single pumping installation operatively connected with said system for providing forced circulation therethrough during periods of low heat transfer and for supplying new liquid to the system simultaneously with the operation of said first means during periods of high heat transfer,;and control means coacting with said single pumping installation for operating the latter to maintain substantially constant liquid flow through the system under all operating conditions.

7. The combination of claim 6 and wherein said single pump installation includes high-pressure booster pumps adapted to operate continuously at full capacity and a jet connected into a the heat-exchanger system so that natural circulation can take place through said jet pump, said jet pump being operatively connected to the Output of the booster pumps for receiving a jet of liquid therefrom, said second means including forced circulation valve means providing communication between the input of said booster pumps and said system to provide forced circulation during periods of low heat transfer, and said first means including supply valve means for providing communication between the input of said booster pumps and a source of feedwater during periods of high heat transfer.

8. The combination of claim 7 and wherein said control means is operatively connected in the system for sensing the ,condition of the fluid flowing therethrough, said control means being operatively connected to said forced circulation valve means and said supply valve means for automatically closing the latter and opening the former during periods of low heat transfer and closing the former and opening the latter during periods of high heat transfer.

9. The combination of claim 8 and wherein a bypass valve means communicates with the system and the output of the booster pumps for bypassing the jet pump when a given pressure is reached at the output of the booster pumps.

10. The combination of claim 8 and wherein a subsidiary heat exchanger is situated between said forced circulation valve means and the input of said booster pumps, for preheating feedwater flowing through said supply valve means and for cooling forced circulation liquid delivered through said forced circulation valve means to the input of said booster pumps to. prevent cavitation effects.

11. The combination of claim 8 and wherein a steam drum forms part of said system and an accumulator receiving steam from said steam drum during periods of high heat transfer for providing useful steam which can be constantly withdrawn from said accumulator, said automatic control means being situated between said steam drum and accumulator.

12. The combination of claim 8 and wherein there are a pair of said heat-exchanger systems which respectively have operation at high heat transfer at different times, a single accumulator communicating with both systems for deriving therefrom useful steam which may be withdrawn from said accumulator, a pair of said automatic control means being respectively located in parts both systems which respectively lead directly into said accumulator, and a single forced circulation valve means, supply valve means, and booster pump unit operatively ;connected with both of said systems, each of said control means being operatively connected with the forced circulation valve means and supply valve means and the system including a pair of jet pumps both of which are supplied by the single booster pump unit. 

1. In a method for operating a heat-exchanger system under greatly fluctuating conditions of high and low heat transfer, the steps of operating the system with at least partial natural circulation during high heat transfer, when fluid is withdrawn from the system, and with forced circulation during periods of low heat transfer, operating a single high-pressure booster pump installation continuously at full capacity while providing said forced circulation through said single pump installation during periods of low heat transfer and while providing a combination of natural circulation and replenishing the liquid of the system with said single pump installation during periods of high heat transfer, and providing between the forced circulation and supply of new replenishing liquid to the system, on the one hand, and the natural circulation, on the other hand, a relationship which maintains a substantially constant flow of liquid through the heat exchanger under all operating conditions.
 2. In a method as recited in claim 1 and wherein the booster pump installation has suction and discharge sides maintained at a constant differential pressure under all operating conditions.
 3. In a method as recited in claim 2 and wherein the speed of operation of the pump installation is regulated to maintain the constant liquid flow in the heat-exchanger system under all operating conditions.
 4. In a method as recited in claim 2 and wherein the system includes a jet pump receiving a jet of liquid from said single pump installation and also receiving and discharging liquid during natural circulation, the step of controlling the operation of said jet pump to contribute to the maintenance of the constant liquid flow through the heat exchanger system.
 5. In a method as recited in claim 4, the step of bypassing the jet pump when the pressure of liquid pumped by said single pump installation rises to a given value.
 6. In an apparatus for deriving steam from a fluctuating heat source, a heat-exchanger system operating under conditions of great fluctuation between high and low heat transfer, first means for operating the system with at least partial natural circulation during the high heat transfer condition, providing useful steam which can be withdrawn from the system, and second means for operating the system with forced circulation during the low heat transfer condition, said second means including a single pumping installation operatively connected with said system for providing forced circulation therethrough during periods of low heat transfer and for supplying new liquid to the system simultaneously with the operation of said first means during periods of high heat transfer, and control means coacting with said single pumping installation for operating the latter to maintain substantially constant liquid flow through the system under all operating conditions.
 7. The combination of claim 6 and wherein said single pump installation includes high-pressure booster pumps adapted to operate continuously at full capacity and a jet connected into a the heat-exchanger system so that natural circulation can take place through said jet pump, said jet pump being operatively connected to the output of the booster pumps for receiving a jet of liquid therefrom, saiD second means including forced circulation valve means providing communication between the input of said booster pumps and said system to provide forced circulation during periods of low heat transfer, and said first means including supply valve means for providing communication between the input of said booster pumps and a source of feedwater during periods of high heat transfer.
 8. The combination of claim 7 and wherein said control means is operatively connected in the system for sensing the condition of the fluid flowing therethrough, said control means being operatively connected to said forced circulation valve means and said supply valve means for automatically closing the latter and opening the former during periods of low heat transfer and closing the former and opening the latter during periods of high heat transfer.
 9. The combination of claim 8 and wherein a bypass valve means communicates with the system and the output of the booster pumps for bypassing the jet pump when a given pressure is reached at the output of the booster pumps.
 10. The combination of claim 8 and wherein a subsidiary heat exchanger is situated between said forced circulation valve means and the input of said booster pumps, for preheating feedwater flowing through said supply valve means and for cooling forced circulation liquid delivered through said forced circulation valve means to the input of said booster pumps to prevent cavitation effects.
 11. The combination of claim 8 and wherein a steam drum forms part of said system and an accumulator receiving steam from said steam drum during periods of high heat transfer for providing useful steam which can be constantly withdrawn from said accumulator, said automatic control means being situated between said steam drum and accumulator.
 12. The combination of claim 8 and wherein there are a pair of said heat-exchanger systems which respectively have operation at high heat transfer at different times, a single accumulator communicating with both systems for deriving therefrom useful steam which may be withdrawn from said accumulator, a pair of said automatic control means being respectively located in parts both systems which respectively lead directly into said accumulator, and a single forced circulation valve means, supply valve means, and booster pump unit operatively connected with both of said systems, each of said control means being operatively connected with the forced circulation valve means and supply valve means and the system including a pair of jet pumps both of which are supplied by the single booster pump unit. 